The term radiosurgery refers to a procedure in which intense and precisely aimed doses of radiation are delivered to a target region in a patient, in order to destroy tumor cells or otherwise treat the target region. The term radiotherapy refers to a procedure in which radiation is applied to a target region for therapeutic, rather than necrotic, purposes. The amount of radiation utilized in radiotherapy treatment sessions is typically about an order of magnitude smaller, as compared to the amount used in radiosurgical sessions. For convenience, the term “radiosurgery” in this application shall henceforth mean “radiosurgery and/or radiotherapy.” Both radiotherapy and radiosurgery are referred to herein as “therapeutic radiation treatments.”
In radiosurgery, it is necessary to control the position of the radiation source so that its beam or beams can be precisely directed to the target tissue while minimizing irradiation of surrounding healthy tissue. It is also necessary to determine with precision the position of the target region (and surrounding critical structures) relative to the reference frame of the treatment device.
The patient is usually placed on a support device, such as a couch or a table. During treatment, if an imaging system is provided, it repeatedly measures the position and orientation of the target relative to the x-ray source. The patient is then positioned by the support device controlled automatically or manually by an operator, so that the treatment target inside the patient body is aligned with respect to an iso-center of the radiation source to ensure that therapeutic radiation is applied to the treatment target within the patient.
It is required that the iso-center of the target treatment area be defined and positioned accurately in order to provide the desired treatment. One method currently used to identify the tumor position for treatment is through the use of a diagnostic x-ray or fluoroscopy system to define and align the iso-center of the treatment area to the iso-center of the radiation source.
While operating these image-guided systems, it is necessary to adjust the position and orientation of the patient in order to ensure that the target within the patient remains properly aligned with respect to the treatment beam. The position and orientation of the patient must be periodically adjusted, for example, in order to compensate for any motion (such as respiratory motion, sneezing, or shifting) that the patient may undergo during treatment. In the currently used image-guided systems, the image of the patient or the treatment area and the ambient area has to be taken many times during the operation to detect any misalignment of the iso-center of the treatment area from the iso-center of the therapeutic treatment system caused by patient movement, and to adjust the alignment.
Therefore, it is desirable to provide a new system for defining and positioning a treatment target with respect to the iso-center of the therapeutic treatment system that minimizes and optimizes the processes required for accurately positioning the patient during the operation.